fix(utc/locale): close Theme 2 — 8 UTC / time / locale findings

UTC invariant + culture-safety fixes across UI form binding, audit entity
hydrate, and locale-dependent parses. Highlights:
- CentralUI-026/027: AuditFilterBar / SiteCallsReport / NotificationReport /
  EventLogs now apply SpecifyKind(Local) + ToUniversalTime() at form submit
  so browser-local datetime-local inputs aren't silently treated as UTC.
- Commons-019: AuditEvent.OccurredAtUtc / IngestedAtUtc init-setters
  re-tag any incoming DateTime as Kind=Utc, documenting the invariant.
- CD-018: AuditLogEntityTypeConfiguration adds UTC ValueConverters on the
  *Utc DateTime columns so EF hydrate yields Kind=Utc (SQL Server's
  datetime2 has no Kind metadata, so reads were returning Unspecified).
- CD-020: GetPartitionBoundariesOlderThanAsync now SpecifyKind(Utc) on the
  raw-ADO read, matching the existing defence in AuditLogPartitionMaintenance.
- SEL-021: EventLogQueryService.DateTimeOffset.Parse now uses
  InvariantCulture + AssumeUniversal | AdjustToUniversal.
- SR-023: Convert.ToDouble in ScriptActor + AlarmActor (4 sites) now
  passes InvariantCulture so non-US locales don't mis-parse string values.
- HM-020: CentralHealthAggregator.MarkHeartbeat anchors LastHeartbeatAt to
  max(receivedAt, now) on offline→online so a stale receivedAt can't
  leave a recovered site one tick from re-going-offline.

3 new tests added (AuditLog UTC converter, AuditFilterBar/EventLogs/
NotificationReport-touching CentralUI tests already cover Apply paths,
heartbeat offline→online). Build clean; ConfigurationDatabase 236,
Commons 330, HealthMonitoring 71, SiteRuntime 301, SiteEventLogging 50,
CentralUI 50 — all green. README regenerated: 104 open (was 112).

src/ScadaLink.CentralUI/Components/Pages/Monitoring/EventLogs.razor

@@ -258,8 +258,12 @@
             var request = new EventLogQueryRequest(
                 CorrelationId: Guid.NewGuid().ToString("N"),
                 SiteId: _selectedSiteId,
-                From: _filterFrom.HasValue ? new DateTimeOffset(_filterFrom.Value, TimeSpan.Zero) : null,
-                To: _filterTo.HasValue ? new DateTimeOffset(_filterTo.Value, TimeSpan.Zero) : null,
+                // CentralUI-027: <input type="datetime-local"> binds with DateTimeKind.Unspecified
+                // — the value is the operator's browser-local wall-clock. Tag it Local and
+                // convert to UTC; the prior code labelled the local value as UTC, silently
+                // shifting the query window by the operator's UTC offset.
+                From: LocalInputToUtc(_filterFrom),
+                To: LocalInputToUtc(_filterTo),
                 EventType: string.IsNullOrWhiteSpace(_filterEventType) ? null : _filterEventType.Trim(),
                 Severity: string.IsNullOrWhiteSpace(_filterSeverity) ? null : _filterSeverity,
                 InstanceId: string.IsNullOrWhiteSpace(_filterInstanceName) ? null : _filterInstanceName.Trim(),
@@ -289,6 +293,18 @@
         _searching = false;
     }
 
+    /// <summary>
+    /// CentralUI-027: convert a value bound from <c>&lt;input type="datetime-local"&gt;</c>
+    /// (DateTimeKind.Unspecified, operator's browser-local wall-clock) into UTC. Must tag
+    /// the value Local before <see cref="DateTime.ToUniversalTime"/> can do anything.
+    /// </summary>
+    private static DateTimeOffset? LocalInputToUtc(DateTime? value) =>
+        value.HasValue
+            ? new DateTimeOffset(
+                DateTime.SpecifyKind(value.Value, DateTimeKind.Local).ToUniversalTime(),
+                TimeSpan.Zero)
+            : (DateTimeOffset?)null;
+
     private static string GetSeverityBadge(string severity) => severity switch
     {
         "Error" => "bg-danger",